Drill hole plugs

ABSTRACT

A grout plug  10  for plugging a drill hole  20  in a mine. The plug  10  comprises an elongate sleeve  12  of porous material adapted to be received in a drill hole  20  and a volume of dry grout material  14  in particulate form. The plug  10  also comprises a liner  16  of water-soluble material, the liner  16  being provided within the porous sleeve  12  for containing the grout material  14  within the porous sleeve  12  in its dry form. In use, when the plug  10  is exposed to water the liner  16  dissolves and the water mixes with the grout material  14  to form a slurry which can seep through the porous sleeve  12  when the plug  10  is tamped into the drill hole  20  to block the drill hole  20  when the grout material  14  cures. A related clay plug is also described having a central core of substantially solid material of low permeability which forms a substrate against which the clay material may cure.

FIELD OF THE INVENTION

The present invention relates to mining, and more specifically blockingoff mining exploration drill holes. The invention has particularapplication for blocking off underground diamond drill explorationholes, however the product may also be applied to surface drill holes.

BACKGROUND TO THE INVENTION

Once underground access is commenced through a portal or shaft for a newmine, diamond drill crews begin drilling from the first availableunderground location to allow geologists to better define the ore bodyso that the design of the mine can be optimised. Therefore explorationdrilling usually occurs in advance of the mine development, andtypically the exploration drill holes range from horizontal to downwarddipping to delineate the ore body beneath and to the side of the mainaccess.

When these exploration drill holes are abandoned, they leave an openhole between the main access and the ore body location which will atsome stage be advanced upon. At a later date when the mine does advanceacross the path of the exploration drill hole, there is a danger thatwhen firing of explosives occurs gases and other debris will rifle backup through the open hole connecting the two locations. This presents aserious safety hazard to any occupants of the mine. There are three waysa Mine Manager may deal with this situation:

-   -   (i) Ensure the mine is fully evacuated prior to firing. This is        not practical in most larger mines where multiple firings occur        during the allotted firing time.    -   (ii) Ensure all intersections are planned and anticipated. This        is difficult due to variation between a hole's expected location        and its actual location. These exploration holes may be hundreds        of meters long and while they are logged the accuracy of the        logging is not necessarily dependable to the extent of knowing        exactly when the hole will be advanced upon.    -   (iii) Ensure all potential exploration drill holes are blocked        off to prevent the danger of rifling.

Prior art methods for plugging exploration drill holes (or in fact anymining holes) include various mechanical devices and/or grouting.

U.S. Pat. No. 3,756,316 (Van Ruth) describes a mechanical bore hole plugwhich can be passed through a drill stem to plug a bore hole. A varietyof these kinds of plugs are available as can be seen athttp://www.vanruth.com.au/default.htm. These plugs are not suitable toblock an exploration drill hole on their own to prevent rifling.Specifically, they are designed for static forces whereas an explosiveintersection of a diamond drill hole results in substantial dynamicforces. There is a substantial risk that the plug will blow out andbecome a projectile, particularly since it is only anchored in the verycollar of the hole where there is often broken ground.

Various other kinds of “packer” are available which are similar to theVan Ruth plug in that they are mechanical devices for plugging a drillhole. They are also referred to as Margo plugs in Canada. A packer maybe made with a longer stem which would place its rubber anchor furtherin the hole so that it is less affected by the broken ground at thecollar. Even so, the same criticisms apply as to the Van Ruth plugabove; it is dangerous to use a packer to protect from rifling whensubject to dynamic forces.

Both types of mechanical devices are designed to transmit grout, andonly when the hole has been grouted through these plugs and the grouthas cured will it be safe from rifling or venting. However, there isconsiderable expense involved in doing this, including the cost of themechanical plug itself, the installation of the mechanical plug byknowledgeable staff, and then the grouting through the mechanical plugby an experienced grout crew using a conventional grout machine.

Grouting the full length of exploration drill holes is not practical,where holes may be up to 200 m or more in length, and those that areangled upward beyond 30 m or so are technically impossible to grout fulllength. An alternative therefore is to grout the collar of the holewhich will effectively prevent rifling. “Grout” is a term that is usedto refer to cementitious slurries used in mining which may cure to astrength similar to that of concrete (harder, but typically morebrittle). A basic grout may be as simple as a mixture of Portland cementand water. Grout is mostly used for ground support in mining whichinvolves anchoring a tendon into a hole that has been drilled in thesurrounding rock for stabilisation of the strata above and around mineexcavations. For this purpose grouts tend to have additives included inaddition to Portland cement, such as plasticisers to increase fluidityand reduce the hydration requirement for curing, accelerators orretarders to reduce or delay curing time, and additives to improve bondstrength particularly with reinforcing steel, i.e. ground supportelements.

Occasionally, grout is also used to simply fill voids or prevent highpressure water inflow.

Traditionally grouting is carried out using a grout pump with one of twowater/cement ratios (WC ratio). Greater than 0.35 WC ratio gives a runnyslurry which needs a grouting technique using a breather tube to bleedthe air out. Less than 0.35 WC ratio gives a thick grout mix being theconsistency of toothpaste in which case the operator slowly withdrawsthe pump delivery tube as the grout enters the hole. Generally, thegrout with the lower WC ratio will be the stronger one.

Pumping grout requires continuity of operations. Delays of more than anhour or so results in the grout mix beginning to set in the pump andwill stop the pump from running. Continuity of grouting requires enoughwork for a grouting crew to continue grouting. However, grouting ofexploration drill holes provides only piecemeal work and is inefficientfor an experienced crew unless the crew has other work in that area tocarry on with. The alternative is for grouting to be carried outinefficiently by non-grouting proficient diamond drill crews on an adhoc basis when required, which means that the drill is standing idlewhile they do this.

The present invention was developed with a view to providing a plug andmethod of plugging a mining drill hole that is less susceptible to thedisadvantages of the prior art noted above.

References to prior art in this specification are provided forillustrative purposes only and are not to be taken as an admission thatsuch prior art is part of the common general knowledge in Australia orelsewhere.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided agrout plug for plugging a drill hole in a mine, the plug comprising:

an elongate sleeve of porous material adapted to be received in a drillhole;

a volume of dry grout material in particulate form contained in thesleeve wherein, in use, when the plug is exposed to water it mixes withthe grout material to form a slurry which can seep through the poroussleeve when the plug is tamped into the drill hole to block the drillhole when the grout material cures.

Preferably the porous sleeve is made from a water-absorbent materialwherein, in use, the porous sleeve helps maintain a moist environment inthe hole during curing by wicking moisture to the grout to assist withcuring the grout. Preferably the porous sleeve is made from alightweight, biodegradable mesh material. Preferably the porous sleeveis made from hessian or jute.

Preferably the plug further comprises a liner of water-soluble material,the liner being provided within the porous sleeve for containing thegrout material within the porous sleeve in its dry form and wherein, inuse, when the plug is exposed to water the liner dissolves.

Preferably the liner is in the form of an inner sleeve made from a thinfilm of plastics material which is separate from the porous sleeve.Preferably the sleeve is designed with a curved leading edge forinstallation to assist in guiding the grout plug into a hole of onlymarginally larger diameter.

Preferably the grout plug is cylindrical or sausage shaped, and ispreferably 600 mm in length. The grout plug may be of varying outerdiameters, but preferably the grout plug has an outer diameter of about46 mm, 58 mm, 74 mm or 94 mm.

According to another aspect of the present invention there is provided agrout plug for plugging a drill hole in a mine, the plug comprising:

an elongate sleeve of porous material adapted to be received in a drillhole;

a volume of dry grout material in particulate form; and

-   -   a liner of water-soluble material, the liner being provided        within the porous sleeve for containing the grout material        within the porous sleeve in its dry form and wherein, in use,        when the plug is exposed to water the liner dissolves and the        water mixes with the grout material to form a slurry which can        seep through the porous sleeve when the plug is tamped into the        drill hole to block the drill hole when the grout material        cures.

Typically the porous sleeve is made from a water-absorbent materialwherein, in use, the porous sleeve helps maintain a moist environment inthe hole during curing by wicking moisture to the grout to assist withcuring the grout. Preferably the porous sleeve is made from alightweight, biodegradable mesh material. Advantageously the poroussleeve is made from hessian or jute, which is a low cost,environmentally sustainable material.

Typically the liner is in the form of an inner sleeve received withinthe porous sleeve. Preferably the liner is in the form of an innersleeve made from a thin film of plastics material which is separate fromthe porous sleeve. Alternatively the liner is formed integral to theporous sleeve. Preferably the liner is made from polyvinyl alcohol (PVA)which is a water soluble plastic that dissolves within seconds whenimmersed in water.

Typically the grout material is ordinary Portland cement. However,depending on the application various additives may be added to the groutmaterial or cement as required, such as plasticisers, retarders,accelerators, clays, and aggregates. The grout material may be comprisedchiefly of bentonite clay or other clay, as required.

Preferably the grout plug is cylindrical or sausage shaped, andpreferably is 600 mm in length.

According to a further aspect of the present invention, there isprovided a clay plug for plugging a drill hole, the clay plugcomprising:

an elongate sleeve of porous material adapted to be received in a drillhole;

a volume of dry clay material;

a liner of water-soluble material, the liner being provided within theporous sleeve for containing the clay material within the porous sleevein its dry form; and

a substantially solid central core of low permeability, the central corerunning substantially the length of the plug.

This embodiment has particular application for sealing water flow from adrill hole.

Preferably the central core comprises wood, metal, steel or cured grout.In this embodiment, preferably the clay material is bentonite or othersuitable clay material. The clay is typically in particulate form, orother suitable form.

According to another aspect of the present invention, there is provideda plug system for plugging a drill hole, the plug system comprising oneor more grout plugs of the present invention, in combination with one ormore clay plugs according to the invention.

According to a still further aspect of the present invention there isprovided a method of plugging a drill hole in a mine, the methodcomprising:

filling an elongate sleeve of porous material, adapted to be received ina drill hole, with a volume of dry grout material in particulate form toform a grout plug;

providing one or more of the grout plugs to a mine site ready for use inthe event that a drill hole needs to be blocked;

immersing one or more of the grout plugs in water for a prescribed timeuntil the water mixes with the grout material to form a slurry;

inserting the one or more wetted grout plugs in the drill hole andtamping each grout plug into the drill hole so that some of the groutmaterial squeezes out through the porous sleeve; and

-   -   allowing the grout material to cure so that the one or more        grout plugs block the drill hole.

Preferably the method further comprises the step of maintaining a moistenvironment in the drill hole during curing by employing awater-absorbent material to make the porous sleeve wherein, in use, theporous sleeve assists with curing the grout by wicking moisture to thegrout.

Preferably the method further comprises the step of providing a liner ofwater-soluble material, the liner being provided within the poroussleeve for containing the grout material within the porous sleeve in itsdry form and wherein, in use, when the plug is immersed in water it isallowed to soak for the prescribed time until the liner completelydissolves.

Throughout the specification, unless the context requires otherwise, theword “comprise” or variations such as “comprises” or “comprising”, willbe understood to imply the inclusion of a stated integer or group ofintegers but not the exclusion of any other integer or group ofintegers. Likewise the word “preferably” or variations such as“preferred”, will be understood to imply that a stated integer or groupof integers is desirable but not essential to the working of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature of the invention will be better understood from the followingdetailed description of several specific embodiments of grout plug andmethod of plugging a mining drill hole, given by way of example only,with reference to the accompanying drawings, in which:

FIG. 1 illustrates a preferred embodiment of a grout plug in accordancewith the present invention;

FIG. 2 is a cut-away section view of the grout plug of FIG. 1;

FIG. 3 illustrates a first step in the process of constructing the groutplug of FIG. 1;

FIG. 4 illustrates a second step in the process of constructing thegrout plug of FIG. 1;

FIG. 5 illustrates how the grout plug in accordance with the presentinvention can be used to prevent rifling and venting in undergroundexploration drill holes;

FIGS. 6 and 7 illustrate a preferred method of installing the groutplugs in accordance with the present invention in a drill hole; and

FIG. 8 illustrates a second preferred embodiment of a clay plug inaccordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A preferred embodiment of grout plug 10 in accordance with theinvention, as illustrated in FIGS. 1 and 2, comprises an elongate sleeve12 of porous material adapted to be received in a drill hole (see FIG.5). The porous sleeve 12 contains a volume of dry grout material 14 inparticulate form. When the plug 10 is exposed to water it mixes with thegrout material 14 to form a slurry which can squeeze through the poroussleeve when the plug is tamped into the drill hole. In this way thegrout plug 10 can be used to block the drill hole once the groutmaterial 14 cures.

Preferably the grout plug 10 further comprises a liner 16 ofwater-soluble material. The liner 16 is provided within the poroussleeve 12 for containing the grout material 14 within the porous sleeve12 in its dry form. In use, when the plug 10 is exposed to water, theliner 16 dissolves and the water mixes with the grout material 14 toform a slurry. The slurry can seep through the porous sleeve when theplug 10 is tamped into the drill hole to block the drill hole when thegrout material cures.

Typically the porous sleeve 12 is made from a water-absorbent materialwherein, in use, the porous sleeve 12 helps maintain a moist environmentin the hole during curing by wicking moisture to the grout material 14to assist with curing the grout. Preferably the porous sleeve 12 is madefrom a lightweight, biodegradable mesh material. Advantageously theporous sleeve 12 is made from hessian or jute, which is a low cost,environmentally sustainable material. In the described embodiment 18 ozhessian is employed to make the porous sleeve 12.

Typically the liner 16 is in the form of an inner sleeve received withinthe porous sleeve 12. Preferably the liner 16 is made from a thin filmof plastics material which is separate from the porous sleeve 12.Alternatively the liner 16 is formed integral to the porous sleeve 12.Preferably the liner 16 is made from polyvinyl alcohol (PVA) which is awater soluble polymer that dissolves within seconds when immersed inwater.

Typically the grout material 14 is ordinary Portland cement. Howeverdepending on the application various additives may be required such asplasticisers, retarders or accelerators, and aggregates.

A currently preferred process of manufacturing the grout plugs 10 willnow be described with reference to FIGS. 1 to 4. A rectangular, elongatesheet of hessian or jute material 14 is cut and folded in half lengthways as shown in FIG. 3. Then the open side and one end of the sheet 14is stitched together along the stitch line 18 as shown in FIG. 4. Theresulting sleeve 12 is turned inside out to conceal the hem. The sleeve12 is designed with a curved leading edge 26 for installation to assistin guiding the grout plug 10 into a hole of only marginally largerdiameter. The plug 10 still needs to be capable of installation evenwhere the hole may have surface irregularities through deviation orbroken ground.

Preferably the PVA liner 16 is formed in a similar way, either bystitching or heat welding along the open side and one end to form aninner sleeve. The PVA liner 16 is not turned inside out. Assembly issimple and involves inserting the PVA liner 16 into the hessian or jutesleeve 12 and filling it with the dry grout powder 14 (and the centralcore if the configuration requires, as discussed below for the secondembodiment 40). The grout plugs preferably have a bulk density afterfilling with grout of 1.5-2.5 g/cc, more preferably about 1.9 g/cc. Thisis driven by the need for the grout plug to retain its shape forinstallation, and to maintain a low water:cement ratio on immersion.Both sleeves 12 and 16 are then wire tied or cable tied at the open tailend, resulting in the completed grout plug 10 as shown in FIGS. 1 and 2.

The completed grout plug 10 is cylindrical or sausage shaped andtypically is manufactured in lengths of 600 mm, with an outer diameterof about 46 mm (allowing a tolerance of about 2 mm within a drill holewith 48 mm inside diameter, and allowing for bit wear and irregularitieswithin the hole). On tamping, the grout material extrudes through thehessian sleeve 12 to engage more fully with the hole and make up thehole diameter. The outer diameter of the porous sleeve 12 may beselected to suit the nominal drill hole size. Colour-coded hessian maybe used to clearly identify different diameter plugs for ease of use forthe various standard diameter drill holes.

The grout plugs 10 will nominally be 2 mm smaller in diameter than thenew bit size for each of the standard sizes shown below, to allow forbit wear.

Hole Maximum Grout Plug Size Diameter (mm) Diameter (mm) AQ/AX 48 46BQ/BX 60 58 NQ/NX 75.8 74 HQ/HX 96 94

The PVA liner 16 may not be in the form of a separate inner sleeve 16 asin the illustrated embodiment. The liner 16 could be formed integral tothe porous sleeve 12, as a layer on the inside or outside of the sleeve12 which blocks the pores in the porous hessian material. The linerhelps to prevent the grout powder, typically Portland cement, fromleaking through the pores of the porous sleeve 12. However the liner 16could be dispensed with altogether if a degree of leakage of the drygrout material during transport and storage can be tolerated.Alternatively the grout material may be selected to be of a particlesize that cannot easily escape through the pores of the porous sleeve 12in its dry form.

A preferred method of plugging a mining drill hole using the grout plugs10 according to the invention will now be described with reference toFIG. 5. The method preferably comprises filling an elongate sleeve 12 ofporous material, adapted to be received in a drill hole, with a volumeof dry grout material 14 in particulate form to form a grout plug 10 asdescribed above. One or more of the grout plugs 10 are then provided toa mine site ready for use in the event that a drill hole needs to beblocked. Rigidity is provided by using a hessian or jute skin, andleakage of a small amount of grout through this skin during handling isinconsequential in comparison to the advantage gained throughmaintaining simplicity of use and low cost.

When a drill hole 20 is required to be blocked, one or more of the groutplugs 10 is carried down to the diamond drill location 22 (see FIG. 5).Each grout plug 10 is immersed in water for a prescribed time until thewater mixes with the grout material 14 to form a slurry. Soaking thegrout plug 10 until the cessation of production of bubbles, generallyaround 2-3 minutes, dissolves the PVA liner 16 and automatically wetsthe grout to a WC ratio of 0.35, which develops a strong, low shrinkgrout. This avoids the requirement for mixing.

PVA is commonly used in the concreting industry and has a documentedeffect of increasing the strength and decreasing the porosity of thecured product. However for the purpose of this application, the dilutedPVA content of the water in which the grout plugs soaks is unlikely toprovide any advantage. More importantly it will not be detrimental tothe integrity of the cured grout.

One or more wetted grout plugs 10 is then inserted in the drill hole 20and each grout plug is tamped into the drill hole so that some of thegrout material extrudes or squeezes out through the weave of the poroushessian sleeve 12, as shown in FIGS. 6 and 7. Tamping is typically doneusing a rigid plastic tube 24, and is similar to the process used fortamping explosives into a drill hole. Tamping it into the drill hole 20avoids the requirement for pumping, and the time to set up and stripdown a grout pump. The grout quality does not suffer, and in fact theself wetting aspect of the grout plug removes the human error involvedin achieving a certain WC ratio. The grout material is then allowed tocure so that the one or more of the grout plugs block the drill hole.Typically up to five of the 600 mm grout plugs 10 may be tamped into thecollar of the drill hole 22 to form a 3 m plug.

Thus it can be seen that the method of the invention further comprisesthe step of maintaining a moist environment in the drill hole duringcuring by employing a water-absorbent material to make the porous sleeve12. The porous sleeve 12 assists with curing the grout by wickingmoisture to the grout. The method may include the further step ofproviding a liner 16 of water-soluble material as noted above.

The drill hole 20 is effectively sealed off with a 3 m grout plug, beingfive such sausages tamped into place one behind the other, for thepurpose of preventing rifling. Mines would be free to use more or lesssausages as the circumstances dictate. Curing time is achieved with aninitial set at 24 hours, early strength at 7 days and full strength at28 days. A 7 day cure is sufficient to prevent rifling, although earlierset times may be achieved by using alternate cements.

The hessian or jute sleeve 12 is economical, environmentallysustainable, and allows some storage of moisture and the wicking ofmoisture to the grout material 14 to assist with curing the grout. Thecuring of grout is essentially the same as curing concrete. It isassisted by continued hydration, resulting in a stronger end result thanif it cures in a dry environment.

The grout plugs 10 are intended to block exploration drill holes toprevent rifling or venting from blasts at any location along the hole ifthat hole is intersected at a later date. The grout plugs 10 aredesigned to quickly, efficiently and economically make a mine drill holesafe for these circumstances. Additives would generally not be requiredfor this purpose since they will increase the cost and complexity of theproduct where the basic product satisfies the purpose at the lowestcost. The grout plugs 10 according to the first embodiment are notintended to completely seal off the hole 20 from the flow of groundwateror gases but may in some instances be able to do this.

A second embodiment of a clay plug 40 of the invention as illustrated inFIG. 8 resembles the first embodiment in many ways and will not bedescribed in detail. The clay plug 40 comprises an elongate sleeve 42 ofporous material containing a volume of clay material 44 which in thisinstance is bentonite clay (although other clays may also be suitable).The clay plug 40 further includes a liner 46 of water-soluble material,and a substantially solid central core 48 running substantially thelength of the plug. The central core 48 is preferably of lowpermeability and typically made from a substance such as wood, metal,steel or cured grout. The central core 48 forms a substrate againstwhich the clay material may cure or seal. This will prevent the claymaterial from remaining dry at the core of the plug, and will providesurface pressure for the sealing property of the clay.

The clay plug 40 has particular application for sealing water flow froma drill hole. The advantage of using bentonite clay as the “grouting”material in this embodiment is that bentonite clay slowly expands andseals when in contact with water. To be effective in sealing againstflowing water, the bentonite 44 needs to be in a relatively thin annulus(as can be seen in FIG. 8), for example about 10 mm to 15 mm thickness.Therefore to seal a bore hole of 48 to 96 mm diameter a low permeabilitycore needs to be included inside the plug. By way of explanation for a74 mm plug, if the bentonite is 10 mm thick inside, the central coreneeds to be 54 mm (74 mm less two “thicknesses” of 10 mm each for thebentonite). The problem with the bentonite is it will seal itself fromthe water, remaining dry if it is thicker than about 15 mm. In thisinstance it will not provide sealing pressure against the hole becausethe dry bentonite inside does not expand, and in fact it will compresseliminating the sealing pressure from the wet bentonite in contact withthe hole.

It should be noted that in the second embodiment, due to the presence ofnatural water in the drill hole, it is not necessary for the clay plug40 to be immersed in water prior to insertion into the hole (although itis still permissible to do this as it will not be detrimental to the endresult).

It should also be noted that in the case of the second embodiment,tamping is not required as the bentonite exudes through the weave of thesleeve 42 under its own expansion.

A still further aspect of the invention relates to a plug system forplugging a drill hole, such as in a mine. The plug system (not shown inthe drawings) comprises a combination of one or more grout plugs 10 withone or more clay plugs 40. Typically the system has application forsealing water flow from a drill hole. For example, a clay plug 40 withbentonite is firstly placed in a drill hole followed by one or moregrout plugs 10 behind the clay plug. The grout plug(s) then cure behindthe bentonite plug forming a secure seal.

Whilst the invention has been described with particular application toprevent rifling back through exploration drill holes, it is anticipatedthat the invention may also have application in the following additionalmarkets:

-   -   1. grouting surface exploration drill holes to prevent native        fauna from falling down these drill holes in addition to        protection from rifling in mining areas,    -   2. grouting both open pit and underground blast holes to prevent        the escape of explosives where those holes break through into        existing workings,    -   3. grouting the collars of open pit blast holes where a blast        will “sleep” at least overnight, preventing rifling of the        stemming material,    -   4. grouting the collars of Vertical Crater Retreat (VCR) type        blasting to improve the impact of explosives on the development,        and    -   5. assisting in sealing off drill holes to prevent water flow.

Now that preferred embodiments of the plug and a method of plugging amine drill hole have been described in detail, it will be apparent thatthe described embodiments provide a number of advantages over the priorart, including the following:

-   -   (i) Since the plugs are completely prepared off site, where        labour is more economical than on site or underground, they can        be manufactured at low cost and provide an extremely economical        alternate to mixing and pumping the grout on site.    -   (ii) A supply of the grout plugs can easily be kept in storage        at the mine site ready for use when required for blocking a        drill hole.    -   (iii) The hessian or jute sleeve is environmentally sustainable        and its porosity assists with retaining and wicking moisture        during curing.    -   (iv) Tamping the plug extrudes some of the grout material        through the porous sleeve which helps to retain the plug in the        drill hole when the grout cures.    -   (v) Soaking the grout plug for the prescribed time dissolves the        PVA liner and automatically wets the grout to a WC ratio of        0.35, which develops a strong, low shrink grout. This also        avoids the requirement for mixing.    -   (vi) Use of the liner in the grout plug helps to prevent grout        powder (such as Portland cement) from leaking through the pores        of the porous sleeve.    -   (vii) In at least one embodiment of the invention, the plug        assists in sealing off drill holes to prevent water flow.

It will be readily apparent to persons skilled in the relevant arts thatvarious modifications and improvements may be made to the foregoingembodiments, in addition to those already described, without departingfrom the basic inventive concepts of the present invention. For example,whilst hessian or jute has been described as the preferred material formaking the porous sleeve, the porous sleeve may be made from anysuitable material. Therefore, it will be appreciated that the scope ofthe invention is not limited to the specific embodiments described.

1. A grout plug for plugging a drill hole in a mine, the plugcomprising: an elongate sleeve of porous material adapted to be receivedin a drill hole; a volume of dry, cement-based, grout material inparticulate form contained in the sleeve wherein, in use, when the plugis exposed to water it mixes with the grout material to form a slurrywhich can seep through the porous sleeve when the plug is tamped intothe drill hole to block the drill hole when the grout material cures.2-3. (canceled)
 4. A grout plug for plugging a drill hole in a mine asdefined in claim 1, wherein the porous sleeve is made from hessian orjute.
 5. A grout plug for plugging a drill hole in a mine as defined inclaim 1, wherein the plug further comprises a liner of water-solublematerial, the liner being provided within the porous sleeve forcontaining the grout material within the porous sleeve in its dry formand wherein, in use, when the plug is exposed to water the linerdissolves.
 6. (canceled)
 7. A grout plug for plugging a drill hole in amine as defined in claim 1, wherein the sleeve is designed with a curvedleading edge for installation to assist in guiding the grout plug into ahole of only marginally larger diameter.
 8. A grout plug for plugging adrill hole in a mine as defined in claim 1, wherein the grout plug iscylindrical or sausage shaped.
 9. (canceled)
 10. A grout plug forplugging a drill hole in a mine as defined in claim 8, wherein the groutplug has an outer diameter of about 46 mm, 58 mm, 74 mm or 94 mm.
 11. Agrout plug for plugging a drill hole in a mine, the plug comprising: anelongate sleeve of porous material adapted to be received in a drillhole; a volume of dry, cement-based, grout material in particulate form;and a liner of water-soluble material, the liner being provided withinthe porous sleeve for containing the grout material within the poroussleeve in its dry form and wherein, in use, when the plug is exposed towater the liner dissolves and the water mixes with the grout material toform a slurry which can seep through the porous sleeve when the plug istamped into the drill hole to block the drill hole when the groutmaterial cures. 12-13. (canceled)
 14. A grout plug for plugging a drillhole in a mine as defined in claim 11, wherein the porous sleeve is madefrom hessian or jute.
 15. A grout plug for plugging a drill hole in amine as defined in claim 11, wherein the liner is in the form of aninner sleeve received within the porous sleeve.
 16. (canceled)
 17. Agrout plug for plugging a drill hole in a mine as defined in claim 15,wherein the liner is formed integral to the porous sleeve.
 18. A groutplug for plugging a drill hole in a mine as defined in claim 11, whereinthe liner is made from polyvinyl alcohol (PVA) which is a water solubleplastic that dissolves within seconds when immersed in water.
 19. Agrout plug for plugging a drill hole in a mine as defined in claim 11,wherein the grout material is ordinary Portland cement.
 20. A grout plugfor plugging a drill hole in a mine as defined in claim 19, whereinvarious additives are added to the cement such as plasticisers,retarders, accelerators, clays, and aggregates.
 21. (canceled)
 22. Agrout plug for plugging a drill hole in a mine as defined in claim 11,wherein the grout plug is cylindrical or sausage shaped.
 23. (canceled)24. A grout plug for plugging a drill hole in a mine as defined in claim22, wherein the grout plug has an outer diameter of about 46 mm, 58 mm,74 mm or 94 mm.
 25. A clay plug for plugging a drill hole, the clay plugcomprising: an elongate sleeve of porous material adapted to be receivedin a drill hole; a volume of dry clay material; a liner of water-solublematerial, the liner being provided within the porous sleeve forcontaining the clay material within the porous sleeve in its dry form;and a substantially solid central core of low permeability, the centralcore running substantially the length of the plug.
 26. A clay plug forplugging a drill hole as defined in claim 25, wherein the central corecomprises wood, metal, steel or cured grout.
 27. A clay plug forplugging a drill hole as defined in claim 25, wherein the clay materialis bentonite.
 28. A plug system for plugging a drill hole, the plugsystem comprising one or more grout plugs; the plug comprising: anelongate sleeve of porous material adapted to be received in a drillhole; a volume of dry, cement-based, grout material in particulate formcontained in the sleeve wherein, in use, when the plug is exposed towater it mixes with the grout material to form a slurry which can seepthrough the porous sleeve when the plug is tamped into the drill hole toblock the drill hole when the grout material cures; and, in combinationwith one or more clay plugs according to claim 25 of the presentinvention.
 29. A method of plugging a drill hole in a mine, the methodcomprising: filling an elongate sleeve of porous material, adapted to bereceived in a drill hole, with a volume of dry, cement-based, groutmaterial in particulate form to form a grout plug; providing one or moreof the grout plugs to a mine site ready for use in the event that adrill hole needs to be blocked; immersing one or more of the grout plugsin water for a prescribed time until the water mixes with the groutmaterial to form a slurry; inserting the one or more wetted grout plugsin the drill hole and tamping each grout plug into the drill hole sothat some of the grout material squeezes out through the porous sleeve;and allowing the grout material to cure so that the one or more groutplugs block the drill hole. 30-35. (canceled)